One such prior art method consists in filling the protective chamber with a material that permits the required relative movements of the operative parts while preventing the extenral medium from coming into contact with the operative surfaces.
One such filler material is a grease of sufficient thickness to prevent it from escaping via the above-mentioned play. Unfortunately, under adverse conditions, e.g. including large variations in temperature at high pressures, experience shows that grease escapes progressively thus progressively admitting the aggressive medium, e.g. abrasive particles.
Another known filler material is oil, and preferably a highly viscous oil. A flexible sealing ring is then used to close the play at the outlet. Unfortunately, known sealing rings deteriorate rather rapidly under the effects of temperature variations and impacts from abrasive particles.
Preferred implementations of the present invention protect a limited-displacement mechanical system against an aggressive medium in a simple and long-lasting manner which is reliable, even when the aggressive medium is subjected to large variations in pressure and in temperature and conveys abrasive particles.